Attention is directed to a Master of Science thesis by one of the inventors, J. L. Dohner, entitled "An On-Line Measurement of Particle Dispersion in Polymer Melts" submitted to Massachusetts Institute of Technology, which will become available to the public upon the filing of this application. This thesis is incorporated herein by reference.
In the plastics industry, additives are often mixed with polymers to produce a plastic with a desired set of material properties. For example, carbon black is mixed with polyethylene to protect the polyethylene from ultraviolet radiation. Titanium dioxide is used with many polymers to act as an opacifier, and polypropylene and polyethylene are mixed to produce an inexpensive high-impact material.
A problem that arises in polymer processing is that the material properties of the final batch are not only a function of the materials being mixed but also a function of the "quality of mixing" in the batch. Two different batches of the same material will have a different set of properties depending on the degree of mixing in each. The elastic modulus, the rate of die swell, the viscosity of the melt, and the cyclic life of the product are a few of the properties affected by the degree of dispersion during processing:
In order for these properties to meet given standards, the melt should be mixed to a given degree. Nevertheless, as the "quality of mixing" improves, the amount of power required to further improve mixing in the melt increases. Thus, the goal of most research in the field of fluid mixing has been to move the state of a melt from an unmixed state to a given state of mixing with a mineral amount of work. The desired state of mixing should not be exceeded.
If it were possible to measure the degree of mixing at the exit of a piece of mixing machinery while mixing was occurring, useful evaluation of the performance of that mixing machinery could be made. There exists a need for an apparatus that would avoid trial and error methods of molding plastic or ceramic parts from fluid precursors. Such a system would also eliminate the time-consuming methods of microscopy presently used to measure mixing in polymer melts and would create a foundation for closed-loop fluid mixing systems for many applications.